The treatment of flowing gases is a common requirement of various industrial processes. For example, contaminated effluent gases are commonly generated by industrial processes and require treatment to remove pollutants prior to being exhausted into the atmosphere. While the present invention will be described in connection with a pollution control system, those skilled in the art will appreciate that the invention has application to other systems which require the treatment or processing of flowing gases, particularly high volume gas flows.
Many air pollution treatment systems include a variety of stages, with effluent gases flowing through ducts from one treatment stage to another en route to being discharged. For a variety of reasons, e.g., in order to save space, to avoid settling of dust in horizontal ducts, or because certain treatment processes work best when the gas flow is oriented in a particular way, the gas flow often must be redirected as it moves through the system. Specifically, it is often necessary for the gas flow to make an abrupt or "hard" turn, i.e., greater than 30.degree., prior to the entrance to the treatment device. Many treatment devices operate most efficiently when the gases flow uniformly from the inlet of the device. This presents a difficult problem when the gas flow must be redirected, sometimes by as much as 180.degree., prior to entering the treatment stage. Where there is a large volume and relatively high flow rate of gases moving through a treatment system, redirecting the gas flow can create substantial non-uniformities in the flow.
For example, a commonly used device in an air pollution control system is a gas conditioning tower ("GCT"). In a GCT water is injected into a flow of hot gases to reduce the temperature and to humidify the gases. A GCT might be used, for example, to condition gases prior to treatment in an electrostatic precipitator where dust particles are removed. In a GCT, gases normally flow vertically from top to bottom, with water being injected into the gas flow near the upper, entrance end of the tower. The time required to evaporate the water spray can be calculated with considerable accuracy if the gas flow is uniform and the spray droplet size distribution is known. However, if the gas flow is not uniform, the calculation becomes much more difficult, and the efficiency of the system is reduced. Non-uniform gas flow results in non-uniform distribution of the spray within the gas flow, non-uniform transit time of the gases through the GCT, coalescence of the spray droplets and consequently inefficient operation of the system.
FIG. 3 is a depiction of the gas flowing at various locations through a GCT 10 with a prior art inlet 5 calculated using computer modeling. Inlet 5 to GCT 10 of FIG. 3 merely redirects the gas flow 180.degree. from vertically upward to vertically downward at the entrance to the GCT. Vectors 50 show the direction and speed of the gas flow at the various locations in the system. As can be seen, the gases are very poorly distributed in the GCT, particularly at the entrance to the GCT, with some of the gas flow being in the upward direction opposite to the overall downward flow. The non-uniformity of the gas flow through the prior art GCT degrades the efficiency, operation and performance of the system.
One prior art solution to flow non-uniformity is to use a series of baffles. This approach, however, has the disadvantage of impeding the gas flow, requiring the use of greater energy to move the gases through the treatment system. Baffles also tend to require greater maintenance due to the collection of dust on the baffle surfaces. Dust build-up also degrades performance.
Accordingly, there is a need for an inlet to a gas processing system which is capable of changing the direction of the gas flow in a compact space and introducing the gas flow substantially uniformly into the entrance of a gas processing system.
Another object of the present invention is to avoid the need to use means for improving flow uniformity which substantially impedes gas flow through the system.
Another object of the present invention is to enable the repositioning of the spray nozzles in a GCT closer to the entrance.